It's up to her if that's the image she wants to portray (Although I doubt it was solely her idea, Christina Aguilera and Britney Spears were marketed in the same way after they finished with Disney).
I personally do think though, that since she still has a large following of children, most of whom would have been watching the VMAs, she should feel a bit more responsibility to be sensible and leave this stuff up to the Lady Gagas of the music industry. I'm not being conservative, I'm just considering with all of this current unpleasantness around stuff like 'sexting', teenagers becoming sexually active at really young ages, watching porn in school ETC., it wouldn't do any harm for celebrities with a young following to be a bit more clean, like people like Taylor Swift or One Direction.